We bring you a Nightline investigation that affects millions of Americans. It's one of the most popular pills on the market today but are reporting suggests that using it can increase the risk of dangerous side effects that may even cause death. In young otherwise healthy patients. We Begin with a story of a 24 year old woman who's convinced that this drug. Is the reason she nearly died and ended up blind -- is among the mounting claims that have prompted an FDA investigation. Here's ABC's chief -- justice correspondent Chris Cuomo. In 2007 Caruso over Sox had started a new pediatric nursing job. Christmas Day her boyfriend surprise -- work and marriage proposals. She wanted to look her best for the wedding. And says she -- commercials suggesting help. And bloating and -- -- and it sounds like a miracle drug. -- -- He has as the birth control of choice for women desperate for relief from severe PMS. But two months later Caruso -- legs started to -- she had worked a long shift -- didn't think much of it but by the next evening she was gasping for air. Her fiance called 911. On the way to the hospital. Chris' heart stopped. Four minutes no heartbeat. Also known as dead to us right. -- had massive blood clots in both lungs her coma lasted almost two weeks. But the damage will last forever right now. Can you see me now. Can you see anything. And that's how you woke -- yes. The big question was -- as the cause of the clotting her coma and her blindness. All birth control pills come with some risk. Two to four women per 101000 will suffer blood clots and some will die as a result. Yet has had generated buzz touting it as the new PMS spill -- news segments like this one. A miracle pill that gets rid of most of the uncomfortable symptoms of PMS. Sales rocketed to nearly two billion dollars a year making it the company's top selling drug. Internal documents obtained by ABC news showed the -- reactions of some executives. This is outstanding. And we get Good Morning America to do the same segment T He. The FDA. Was not a news. Yet He wants to -- fifty points and they say Diaz was not shown to be effective for common PM -- just a rare and serious form of menstrual symptoms. The company denied wrongdoing but agreed to spend twenty million dollars on corrective bats. You should know that yes for the treatment of premenstrual disorder disorder or PM ET and moderate -- Not for the treatment PMS or mild with. Yet by then millions of women had already switched to yes. Bear cites its own studies as proof that yet as is just as safe as other birth control pills. But several independent studies have put -- as his risk. Two to three times higher. Doctor Suzyn -- authored and. Independent study involving a million women the two -- is sponsored studies found no difference in risk laden for independent -- -- increased risks she says she sent her findings to bear. But they didn't respond. This studies -- -- -- increased risks and not in the best interest of the company. Thousands of women are now suing -- including Caruso -- Sox but the company denies any wrongdoing citing those lawsuits -- refused to be interviewed. And instead sent us a statement. Saying yeah as is as safe as any other birth control pill. When used correctly. So we called to press for answers. Why aren't. You putting someone in the chair with something as important this. -- -- Shouldn't I asked. Him. But we had already sent them detailed questions but you don't wanna just discuss it. And when we repeatedly call back. And no answer from bear. And no answers -- -- whose life is changed forever. Everything that I five's. -- for -- so hard for. Has disappeared. -- not a pediatric nurse right now no I'm not you don't have the future you thought you're going to happen. You're not engaged anymore now -- can you believe. It all happen. And started with a pill called yet to -- Our thanks to Chris Cuomo -- that investigation. The FDA meanwhile is now reopening the case on -- as conducting its own new review of the drug safety. And if you're considering your birth control options experts say you should as always consult your own doctor.

This transcript has been automatically generated and may not be 100% accurate.

Yaz More Risky Than Other Leading Birth Control Pills?

ABC News investigates the drug maker of the popular birth control pill.

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